Tank Slappers

Originally Posted by Flamin_Squirrel

Lean angle has absolutely nothing to do with it though, so it could quite easily be the cats eye.

The only time I've had even slight wobbles of the bars (and up to almost complete tank slappers), the bike has been leant over. I've hit many a cats-eye with the bike upright, as I've posted before, with no ill effects at all.

Surely that can't be luck though.

Not knowing much about tank slappers, I did a little googling, maybe of use to this thread as a whole:

Now consider what happens when a motorcycle's front wheel leaves the ground temporarily, such as when the rider pops a wheelie or accelerates sufficiently such that full contact of the front tyre with the road surface is lost momentarily. If the wheel is still aligned with the direction of travel when it touches back down there's no problem. In fact, the gyroscopic force created by the rotation of the front wheel tends to ensure this. If, however, the alignment is lost, a tankslapper may happen.

I'd argue that it's harder to keep the front wheel lined up with direction of travel whilst mid corner, partly because the bike is leant over. Probably wrong though.

Originally Posted by Baph

Probably wrong though.

As usual, yes.

Search some video of anyone landing a wheelie crossed up to see why.

Originally Posted by Flamin_Squirrel

As usual, yes.

Search some video of anyone landing a wheelie crossed up to see why.

Agreed, wheel is out of alignment with the direction the bike is going. Seen that before.

Like I said though, mid corner, harder to keep the wheel lined up if it looses contact/slips/holding too tight etc. Also the contact patch isn't the same as when straight, so forces through the wheel are changed as well.

Correct me if I'm wrong, but don't most tank slappers happen mid corner? Certainly most of the one's I've seen do. I'm not saying they ALL do though, nor saying that just the corner causes it.

Well, i think baph is right. This is my thinking; when a rotating mass (front wheel then) is travelling upright (perpendicular to the plane of the road) and straight then the rotating mass is stable i.e. not prone to oscillations. When that object is lent over slightly (so less than 90 degrees) then the chances of an oscillation of the handlepbars increase (think about how a wheel lent over just wants to keep falling onto its side; and how a rotating wheel lent over wants to go into a spiral) because the rider is trying to fight it. Hit a bump mid-corner and the energy of the rider trying to fight it coupled with the bump setting the wheel stright can induce the tank-slapper. Everyone think waaaay back to the tl1000s, which tank slapped its way through journos like it was a chav seeking an ASBO. This happened alot on bumpy B-roads exiting corners

Now, in addition, when the wheel is off the floor, and rotating, and pointed at some angle away from the line of travel, then when the wheel lands on the floor, the energy of this can cause the unwanted oscillations, since it acts sort of like a spring (the force of the landing straitening the wheel pushes it past the center equilibrium point and to the other side, until the energy disipates).

In both cases, a tank-slapper can occur.

This is my thinking, anyway.

Matt

I did wonder for a while what tank slappers were- firstly, I thought they were when you come off the revs/brake too hard and slap the delicates on the tank. Was later informed by my bro the true nature of the beast- have to say it'd scare the willies out of me too.

I had concluded, though, that it had nothing to do with very obviously promiscuous ladies and military hardware.

Originally Posted by alpinestarhero

Well, i think baph is right. This is my thinking; when a rotating mass (front wheel then) is travelling upright (perpendicular to the plane of the road) and straight then the rotating mass is stable i.e. not prone to oscillations. When that object is lent over slightly (so less than 90 degrees) then the chances of an oscillation of the handlepbars increase (think about how a wheel lent over just wants to keep falling onto its side; and how a rotating wheel lent over wants to go into a spiral) because the rider is trying to fight it. Hit a bump mid-corner and the energy of the rider trying to fight it coupled with the bump setting the wheel stright can induce the tank-slapper. Everyone think waaaay back to the tl1000s, which tank slapped its way through journos like it was a chav seeking an ASBO. This happened alot on bumpy B-roads exiting corners

Now, in addition, when the wheel is off the floor, and rotating, and pointed at some angle away from the line of travel, then when the wheel lands on the floor, the energy of this can cause the unwanted oscillations, since it acts sort of like a spring (the force of the landing straitening the wheel pushes it past the center equilibrium point and to the other side, until the energy disipates).

In both cases, a tank-slapper can occur.

This is my thinking, anyway.

Matt

You're overthinking this one...

Originally Posted by alpinestarhero

the wheel is off the floor, and rotating, and pointed at some angle away from the line of travel

That's the only bit that's important, and can happen when you're bolt upright, or lent over.

[21QUEST]

Originally Posted by Flamin_Squirrel

You're overthinking this one...



That's the only bit that's important, and can happen when you're bolt upright, or lent over.

Guys, FS is right you know. No need to overthink

Mmmh slappers...

on my ZX6R i had a tank slapper coming over the top of a hill while accelerating hard, front wheel left the floor slightly turned a little bit and hey-presto big ol' tankslapper really is quite scarey it can happen in a straight line as much as it can in a corner ...

Thanks for all the advice guys (i'm still a new rider really - only passed in Nov 05) To be honest - i think it's a case of "idiot rider" this time. I'm usually quite sensible aren't i Dave - but everyone was up ahead & i just felt like catchin up. Scared the C*&p out of me though so don't think i'll be doing that again.

And yes - it was proper tankslapping - not just wobbling. My shoulders and forearms are killing me from the bars violently moving about. I'm just really glad someone was on my side on Saturday or else might not be here to ask what i've done wrong.

Feel more than nervous now though (i'm still recovering from a broken back from snowboarding last year - hence the back protector in the pic - cheers for that unflattering pic by the way dave!!)

Anyway -really appreciate your views/tips/advice/comments etc! Big help. Ta muchly. Helen